Process of making asphaltic material



Patented May 22, 1928.

UNITED STATES PATENT OFFICE.

JOHN D. FOBRESTER, O12 KANSAS CITY, MISSOURI, ASSIGNOR T PETER J.MOINERNEY OF DALLAS, TEXAS.

PROCESS OF MAKING ASPHALTIC MATERIAL.

No Drawing.

This invention relates to improvements,

for making asphaltic road material, and refers more particularly to acombination of an asphaltic binder and crushed stone adapt able for useboth in the binder and surfacing courses of roads or streets.

Among the objects of the invention are to provide a process in which theasphaltic binder is intimately bonded to the crushed stone, a materialwhich .may be shipped in open-topped cars, easily loaded into andremoved from the cars as distinguished from the usual type of asphalticmixes which congeal and set, making it very diflicult without the use ofsteam to unload asphaltic mixtures transported over any considerabledistance.

Describing first the common type of binder course using crushed stoneWithan ,asphaltic binder, the crushed stone, termed as crusher runstone, is preferably limestone, granite or crushed gravel sizedaccording to specification. Normally, for the binder course, stoneranging from one and onefourth (1%) inch to one-fourth inch properlygraded is satisfactory. With this is a filler of fine material of thesame composition sufficiently small in size to pass a one-quarter inchscreen and constituting 3 substantially ten percent of the mix. Withthis is combined from 4% to 5% of asphaltic binder,the same beingthoroughly intermixed with'the rock.

Material for the top course or wearing surface, varying somewhat incharacter from the binder course in that the crushed stone is of smallersize ranging from threefourths inch to one-fourth inch properly gradedmaterial. Vvith a top course the filler or fine material passing aone-fourth inch screen constitutes 20% of the mix and the asphalticbinder from 5% to 7%.

The asphalt specifications will vary with climatic conditions. Throughthe South, in

4 States such as Texas, Alabama and Mississippi, the asphalt penetrationwill range from to 70, while in the North, through Minnesota and theDakotas. the penetration is normally in the neighborhood of 95.

0 Ductility in all cases should not be under 85 at 77 F. This briefexplanation of the characteristics of the binder and top courses used inconnection with asphaltic highways, streets and roads, describes brieflythe char- Application filed June 26, 1925. Serial No. 39,815.

acteristic of the particular ingredients or constituents of the roadmix.

The greatest trouble experienced in handlmg material of this characterand in laymg asphaltic road mixesof this kind, is the fact that itcannot be transported for any considerable distance from the plant where itis prepared without utilizing considerable heat in the way of steam forremoving the -mix from the cars due to the congealing of the asphalt andsetting to form a tough solid mass. The present invention contemplatesthe transporting or conveying of such mixes, as described above, forconsiderable distances in railway cars, truck, or otherwise, due to theuse of a liquefier or a relatively light solvent oil used With a mix fora double purpose, first, to carry the asphalt more effectively into theporous stone assuring a more satisfactory bond between the binder andcrushed stone and at the same time maintaining the asphaltic binder in amore liquid or slushy condition over a considerable period of time priorto its evaporation facilitating the handling of the material until itcan be rolled in place upon a highway or road.

It is recognized that at the present time this practice of using aliquefier or diluent vehicle is used in the preparation with a coldstone mix wherein the crushed rock is combined to the asphalt withoutheating the stone. In fact, at the present time two methods are employedfor mixing crushed stone and asphalt as above described. In

one case, a very satisfactory mix is prepared which is diificult tohandle; in the other case, an eas1ly handled mix is prepared which isnot altogether satisfactory due to the lack of a proper bond between theasphaltic binder and the crushed stone.

Referring now to the first well known method of preparing this as)haltic material, crusher run stone is heate to 500 F. or more toeliminate the moisture. This heating is carried out in any suitable typeof drier. The asphalt binder is then mixe therewith to thoroughlyincorporate the bituminous substance with the crushed rock. Theparticular advantage of a mix of this character is the satisfactory andintimate bond which is effected between the asphaltic binder and thestone due to the removal of the moisture from the stone which increasesits porosity and permits the liquid asphalt to penetrate moreeffectively into the surfaces of the rock. The disadvantage of thismixture is the difficulty in handling when it has cooled due to thesetting and congealing of the asphaltic binder into a tough solid masswhich is impossible to handle except with a pick and can only besuccessfully removed from cars by the use of steam. Another difficultyis encountered in properly rolling this material in place on the roa asit necessitates relatively complete dismtegration before the chunks ofthe'm'aterial can be satisfactorily rolled.

A second well known manner of preparing an'asphaltic crushed stonecombination is that prepared under the name of amesite in which thestone is not heated but prepared and graded cold. To this stone is addeda liquefier which consists of relative- .ly light oils or distillateshaving a Baum gravity of 40 to 52. To this combination is added theasphalt heated to a liquid condition. The liquefier, to a certain extentdissolving the asphalt, renders it more fluid and carries it into thestone to a certain limited extent. The cold stone containingconsiderable moisture has a retardant effect to the penetration of theasphaltic material. The advantage of a mix of this character is,however, that it is easily worked and can be maintained overconsiderable periods of time in a. relatively liquid slushy condition,thus rendering it especially adaptable to road work situatedconsiderable distances from the plant in which it is mixed. Thismaterial ,can be shipped in open-topped cars to any part of the countryand there easily unloaded if a liquefier is chosen which evaporatesslowly. It has been found that by carefully choosing a suitableliquefier and timing its evaporation period with the distance that thematerial is to be trans-- ported, a satisfactory mix which has theproper consistency on the job is produced. The disadvantage of a mix ofthis character, however, is that the presence of moisture in the coldstone prevents a satisfactory bonding or adhesion of the asphalticbinder to the stone.

My present method is an improvement upon the above explained methods inthat I heat the crusher run stone in a drier to a temperature of over200 F., or in no event in the first instance, is dumped into a pug millor other type of mixer in which the liquefier is introduced. Asphaltheated to temperatures of from 250 to 325 F. is then added andthoroughly mixed to the combination of the crushed stone and liquefier.It is advisable that neither the crushed stone nor the asphalt be heatedto the flash point of the liqueiier. the combination of the asphalt,crushe stone and liquefier, a filler material, comprising not ess thanone-half percent or more than one percent of the total weight of themix, is added. This filler material is preferably calcium hydrate oroxide, limestone dust pulverized to the extent that it will pass a twohundred mesh screen, or by draulic cement.

The particular advantages of preparing the mix in this manner are firstthere is removed substantially all of the moisture from the stone whichassures a better bonding between the asphaltic binder and the stone asthe heat in removing the moisture increases the porosity of the stone.The liquefier dissolves to a considerable extent the asphalt, reducingits surface tension and accelerates the penetration of the asphalt intothesurface of the stone and the adhesion of the asphaltic binder to thestone, effecting an intimate bond therebetween. It is particularlyadvantageous to select a liquefier which has a flash point above theboiling point of water in order that the moisture may be moreeffectively removed from the stone without danger of flashing theliquefier. Also, a liquefier having a relatively high flash pointpermits the heating of the asphalt to a more fluid condition in whichcase it is more readily absorbed into the surface of the stone. Asdescribed, a liquefier should be chosen where the mix is to betransported a short distance which will readily evaporate, while in thecase where the mix is to be conveyed for a relatively long distance fromthe plant in which it is prepared, a slowly evaporating liquefierisbetter adapted to such a mix as it maintains the crushed rock andasphalt combination in a slushy condition over a longer period of timeand prevents its congeal1ng,making it diflicult to remove the mix fromthe cars in which it is transported.

While it is recognized that to heat crushed stone and combine it withasphalt or to use a liquefier in preparing a cold crushed stone asphaltmix, is well known in the art, it is thought to be new to prepare a mixin the manner described, that is, heating the crushed stone to atemperature below the flash point of the liquefier, combining theliquefiertherewith, and adding an as haltie binder, thus assuring aproper bon ing of the asphaltic binder and crushed rock by eliminationof the moisture in the rock and After thoroughly mixing efl'ectingan'easily workable mass by the use mixture adapted to be laid cold,comprising the steps of heating graded crushed stone of a liquetier ofthe proper character.

The amount of liquefier used and the char- I acter of the liquefier willvary according to the particular asphalt and the character of thecrushed stone as well as other varying conditions.

A further advantage of my process lies in the fact that a more uniformproduct is produced and better'plant control may be had by drying allthe crushed rock preliminarily to eliminate the moisture. Some rocks arenotoriously deliquescence and rapidly acquire moisture in theatmosphere. Unless such materials are first heat treated or dried, thebonding of the asphalt is very unsatisfactory and stripping and peelingof the binder results.

Crushed stone aggregate is heated to temperatures of from 200 F. to 300F. to substantially eliminate the moisture. To this hot stone is added avolatile oil liquifier, preferably in a closed retort, the liquefierhaving a flash oint about the heat of the stone. Such a liquefier asnaphtha, kerosene, light gas oil, or a combination of theseloils, issatisfactory for this purpose. After being thoroughly combined with theheated rock, the bituminous or asphaltic composition which comprises anasphalt of from 60 to 95 penetration having a ductility normally notless than, 85 at 77, is added, having first been suliiciently heated tofacilitate its handling.

This composition comprises; of from 2.5% to 7% of the final mix.

I claim as my invention:

1. A process of making an asphaltic road mixture, comprising the stepsof preparing the crushed stone aggregate by heating to a temperature toeliminate the moisture there from. adding to the crushed stone while hota light oil having a flash point above the temperature of the dryingheat and finally adding and thoroughly incorporating therewith anasphaltic binder.

. material 2. A process of making an asphaltic road in a drier tosubstantially eliminate the moisture therefrom, adding to the crushedstone while hot a hydrocarbon solvent thereto having a flash point abovethe temperature used in drying the stone and subsequently incorporatingan asphaltic binder to produce a mix of easily workable consistency.

3. A process of making asphaltic road mixture adapted to be handled andlaid cold and remaining at a workable consistency from the time of itspreparation to its application, comprising the steps of heating crusherrun stone in a drier to temperatures above the boiling point of water tosubstantially eliminate the moisture therefrom and increase theabsorbent qualities thereof, adding to the crushed stone while hot ahydrocarbon solyent having a flash point above the temperature used indrying the stone and subsequently incorporating an asphaltic binder toproduce a mix of a predetermined consistency, said solvent adapted toimprove the penetration and bonding effect of the binder with the stone.

4. A process for making an asphaltic road mixture, comprising the stepsof drying the crushed stone by applying heat to remove the moisturetherefrom, adding a lightsolvent to the stone while in the heated stateand subseguently adding an asphaltic binder.

5. rocess for making an asphaltic road comprising the steps of heatinggraded crushed stone in a drier to substantially eliminate the moisturetherefrom, then adding to the crushed stone while in a heated conditiona hydrocarbon solvent having a flash point above the drying temperatureand subsequently incorporating an asphaltic binder to produce a mixofeasily workable consistency.

,JOHN D. FORRESTER.

